1. Field of the Invention
The present invention relates to a photoelectric material and a manufacturing method thereof, a photoelectric device, and a photosensitiser used therefor. More specifically, the present invention relates to a photoelectric material used for a photoelectric device such as a photovoltaic cell, and a manufacturing method thereof.
2. Description of the Background Art
The photoelectric material refers to a material which converts optical energy to electric energy. When the photoelectric material is irradiated with light, electrons bound in the material are released to move freely by the optical energy, whereby free electrons and holes are generated. When the generated free electrons and holes are separated with high efficiency, electric energy can be continuously obtained from optical energy in the photoelectric material. Such photoelectric material is utilized in a solar cell, for example.
Recently, a wet type solar cell using a photosensitising dye and having high conversion efficiency has been attracting widespread attention. Such a wet type solar cell is mainly formed of a semiconductor electrode, a counter electrode and an electrolyte layer held between these electrodes, for example. In the semiconductor electrode, which is the photoelectric material, a photosensitising dye having an absorption spectrum in a visble light range is attached to the surface of the semiconductor. In the cell, when the semiconductor electrode is irradiated with light, electrons are generated on the side of the electrode, and the electrons move through an electric circuit to the counter electrode. The electrons which have moved to the counter electrode are transferred by ions in the electrolyte, and return to the semiconductor electrode. By the repetition of this process, electric energy is taken out.
Japanese Patent Laying-Open No. 1-220380 discloses a solar cell having a photosensitising dye such as a transition metal complex attached to the surface of a metal oxide semiconductor. According to the method of manufacturing the solar cell, the metal oxide semiconductor is dipped in an aqueous solution containing the photosensitising dye at room temperature, whereby the photosensitising dye is attached to the surface of the semiconductor.
International Publication No. WO91/16719 and the corresponding Japanese National Publication No. 5-504023 disclose a photovoltaic cell having a titanium dioxide layer doped with metal ions or boron to which a photosensitiser is applied. In the photovoltaic cell, the photosensitiser includes transition metal complexes wit the ligands being bidentate, tridentate or omnidentate polypyridyl compounds, which may be unsubstituted or substituted, and transition metal complexes with at least one ligand comprising a mononuclear cyano-containing pyridyl compound. In the method of manufacturing such photovoltaic cells, a titanium dioxide semiconductor layer is placed in an ethanol solution containing the photosensitiser, whereby the photosensitiser is attached to the semiconductor layer.
International Publication No. WO94/05025 discloses a photovoltaic cell having a photosensitiser selected from optical brightener compounds and phthalocyanine compounds attached to a titanium dioxide layer. In the method of manufacturing such a photovoltaic cell, the photosensitiser is dissolved in ethanol, and the resulting ethanol solution is used for attaching the photosensitiser to the titanium dioxide layer.
Japanese Patent Laying-Open No. 7-249790 discloses that in a method of manufacturing a photoelectric material used for a solar cell, a photosensitizing dye is adsorbed to the surface of a semiconductor by heating and refluxing a liquid containing the photosensitising dye and the semiconductor. In this publication, it is disclosed that metal phthalocyanine such as copper phthalocyanine and titanyl phthalocyanine, chlorophyll, hemin, complexes of ruthenium, osmium, iron or zinc as disclosed in Japanese Patent Laying-Open No. 1-220380 and in Japanese National Publication No. 5-504023, metal-free phthalocyanine, cyanine dyes, merocyanine dyes, xanthene dyes, and triphenylmethane dyes can be used as the photosensitising dye. Further, this laid-open publication discloses that in manufacturing the photoelectric material, water, alcohols, toluene or dimethyl formamide may be used as a liquid in which the photosensitising dye is dissolved. On the other hand, the laid-open publication discloses only a specific example in which cis-(SCN).sub.2 -bis(2,2'-bipyridyl-4,4'-dicarboxylate) ruthenium (II) is dissolved in ethanol, a glass plate having a titanium oxide film thereon is placed in the ethanol solution, the ethanol solution is heated and retluxed and the dye is adsorbed to the titanium oxade film. The laid-open publication does not provide any support for the possibility of practical use of the photosensitising dyes other than the ruthenium complex in the photoelectric material. Further, the laid-open publication does not provide any information as to whether solvents other than ethanol can be practically used to solve the photosensitising dye in manufacturing the photoelectric material